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Old 11-20-2020, 07:59 AM   #1
Gerald81
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Default Master cylinder larger than 1 1/16 inch / 26.99mm?

Does anyone know if there is an aftermarket or Subaru master cylinder that is larger than the 1 1/16 inch or 26.99mm STI ones?

My car is a 2007 STI which already comes with the 26.99mm ones. After I upgraded the fronts to the STI RA-R 6-pot calipers, the pedal stroke seems to be very slightly softer and longer. I was fine with it for awhile but now I've put on the R205 4-pot calipers on the rears, and the pedal stroke is even softer and longer than before.

Still somewhat driveable, but I was wondering if a slightly larger MC would fix this, given the increase in piston surface area moving from the stock 4/2 setup to 6/4 now?
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Old 11-20-2020, 09:37 AM   #2
snow_bound26
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I believe those are the largest MC Subaru supplied from everything I've read. Have you done the MC brace yet?

Something I've been thinking about is changing the piston clearance from the brake pedal into the MC. I have noticed my pedal has more travel after going from the sliding calipers to my 4/2 brake setup as well.
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Old 11-20-2020, 11:01 AM   #3
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Quote:
Originally Posted by Gerald81 View Post
After I upgraded the fronts to the STI RA-R 6-pot calipers, the pedal stroke seems to be very slightly softer and longer.
Are you sure you bled the brake lines properly?
What did you use for brake fluid?

As snow_bound said, those are the biggest MCs from Subaru.
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Old 11-20-2020, 11:26 AM   #4
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I too would question the bleeding if it was done sufficiently.

I'd adjust the pedal play and add a MC brace as a final touch
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Old 11-20-2020, 11:56 AM   #5
Gerald81
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Thanks guys, I'll check the bleeding but this was done professionally.

I'm using Motul Dot 4 fluid, and already have an MC brace / stopper.

It just seems to me like the pedal stroke is progressively getting longer and softer as I increase the number of pistons / caliper size, from 4/2 to 6/2 and now 6/4, which makes me think the MC size is now too small.

How does one go about adjusting brake pedal play?
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Old 11-20-2020, 12:36 PM   #6
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Go under the dash, look at brake pedal. You'll see some adjustment available on there as well as brake light switch.
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Old 11-20-2020, 05:00 PM   #7
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Quote:
Originally Posted by Gerald81 View Post
Thanks guys, I'll check the bleeding but this was done professionally.

I'm using Motul Dot 4 fluid, and already have an MC brace / stopper.

It just seems to me like the pedal stroke is progressively getting longer and softer as I increase the number of pistons / caliper size, from 4/2 to 6/2 and now 6/4, which makes me think the MC size is now too small.

How does one go about adjusting brake pedal play?
May have been done professionally but was it done correctly?
Was this a Subaru-specific shop?

What about your brake lines? How old are they?Consider SS brake lines. They don't expand like rubber ones do under pressure, especially when they get old.

Google how to adjust Subaru clutch pedal. Very easy. Takes 5 minutes.
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Old 11-21-2020, 12:44 AM   #8
Gerald81
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Yes the works were done at a shop that has done Subarus since the GC8 days.

Brake lines are already SS braided ones.

Would something like the below bolt on for our cars?

https://www.wilwood.com/MasterCylind...o=260-14960-BK
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Old 11-21-2020, 12:37 PM   #9
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You're overthinking the problem.
Why do you think you need another aftermarket MC when the Subaru one works just fine, unless your current MC is failing?

The Subaru MC works w/the Subaru big brakes.

I would go back and talk to whoever did the brake bleeding and talk to them.
Sounds like something was not done right.

Just because they may be a good shop, doesn't mean the didn't put the new kid on the job and this was his first time doing a brake job.
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Old 11-23-2020, 12:51 AM   #10
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Quote:
Originally Posted by Samurai Jack View Post
Why do you think you need another aftermarket MC when the Subaru one works just fine, unless your current MC is failing?
I think he made it pretty clear that he needs it because the pedal feel with his new setup doesn't match what he wants.

Quote:
Originally Posted by Samurai Jack View Post
The Subaru MC works w/the Subaru big brakes.
Just because it works doesn't mean it gives him the pedal feel he wants.

How does the piston areas of the RA-R 6-pots and R205 4-pots compare to what he started with? Is it possible that what he's feeling is actually because the pistons area is, in fact, larger than what he originally had?

Quote:
Originally Posted by Samurai Jack View Post
I would go back and talk to whoever did the brake bleeding and talk to them.
Sounds like something was not done right.

Just because they may be a good shop, doesn't mean the didn't put the new kid on the job and this was his first time doing a brake job.
Apparently they hired two new guys, because he's felt the same effect after two different brake system modifications.
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Old 11-23-2020, 12:14 PM   #11
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If the Subaru MC he is currently using is different than the Subaru MC normally used the the new Subaru brakes he installed, then, yes, he needs to replace the MC with one designed to work with the newer brakes.

AFAWK, the Subaru MCs are the same. We don't know for certain.
If they actually are the same, then it's not the MC unless his current MC has an issue.

We don't always get what we want in life. See comments above.
If they are the same, then he is getting things the way Subaru intended.
If they are the same, then the issue would lie somewhere other than the MC.

I would verify if the Subaru MCs are actually the same, between what he has now and the one that came with the larger brakes. Once that is determined, then and only then would the OP have a better path to resolving the issue.

Just going to an allegedly larger aftermarket MC does not guarantee this will solve the issue.

Has the OP talked to the Subaru shop about this issue?
What did they say?

If not, first place he should have gone.
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Old 11-23-2020, 03:13 PM   #12
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Can one just do the math? measure the piston area, and then use the brake calculator spreadsheet and go to town?
https://forums.nasioc.com/forums/sho...d.php?t=928642

Seems like a pretty easy way to dig into things on your own.
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Old 11-23-2020, 10:32 PM   #13
Gerald81
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Quote:
Originally Posted by Patrick Olsen View Post
I think he made it pretty clear that he needs it because the pedal feel with his new setup doesn't match what he wants.


Just because it works doesn't mean it gives him the pedal feel he wants.

How does the piston areas of the RA-R 6-pots and R205 4-pots compare to what he started with? Is it possible that what he's feeling is actually because the pistons area is, in fact, larger than what he originally had?


Apparently they hired two new guys, because he's felt the same effect after two different brake system modifications.
Thanks Patrick, those are EXACTLY my concerns.

I know everyone's first reaction to this issue is bleeding, etc. I really doubt this is the issue, and in any case the work itself was done by the shop's boss who's been working on Subarus since the GC days, build competition Subarus and owns a Subaru himself.

Also, I have all the usual braking mods such as SS braided hoses, brake stopper, etc.

I did a fair bit of research before pulling the trigger on this upgrade.

Firstly, I noted that the stock GD STI (with 4/2 pots) and the RA-R (with 6/2 pots) both shared the same ancillary braking hardware, i.e. exact same part numbers.

Secondly, I noted that the stock GR STI (with 4/2 pots) and the R205 (with 6/4 pots) both also shared the same ancillary braking hardware.

For the two reasons above, I surmised that Subaru deemed that moving from 4/2 to 6/2 or even 6/4 would not significantly affect pedal feel. However, I personally did feel the difference (however mild) each time I upgraded my brakes, first to 6/2 and now more recently to 6/4.

Doing more research, and also based on my prior experience with a more drastic upgrade from a 1 pot to 4/2 pots setup where the pedal feel/travel really went down the drain, I've come to the conclusion that the MC is somewhat undersized now. I would really like to try a larger one such as a 1-1/8", but only option is aftermarket and I have no idea how to verify if these would be compatible, as I can't find much in terms of specs (e.g. stroke) for the stock MCs apart from the bore size.

I wonder if there are other considerations as well, such as the ABS system which could affect the pedal feel even under normal conditions when the ABS is not activated?
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Old 11-24-2020, 10:19 AM   #14
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What brake pads did you have before and what pads do you have now?

- Andrew
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Old 11-24-2020, 11:22 AM   #15
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Quote:
Originally Posted by Gerald81 View Post
I would really like to try a larger one such as a 1-1/8", but only option is aftermarket and I have no idea how to verify if these would be compatible, as I can't find much in terms of specs (e.g. stroke) for the stock MCs apart from the bore size.
Now that we know that you have determined that the Subaru MCs are the same, it makes things more clear.
Brake bleeding is the simplest thing to check / correct, so usually it's one of the first things brought up. Many people screw it up and have issues like you are describing.

Have you contacted Wilwood and asked their opinion on whether or not their MC would be compatible w/the Subaru brakes you have now?

Since you have confirmed the other items, that's what I would do and see what you can find out.

I just don't want to see you spending the time, effort, and money to buy the Wilwood unit only to find that there is little to no improvement.
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Old 11-25-2020, 02:55 AM   #16
Gerald81
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Quote:
Originally Posted by AndyRoo View Post
What brake pads did you have before and what pads do you have now?

- Andrew
When I was on 6/2 I was using Ferodo DS2500 front and rear.

Now with 6/4 I switched to Pagid RSL 19 front and rear.
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Old 11-25-2020, 02:56 AM   #17
Gerald81
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Quote:
Originally Posted by Samurai Jack View Post
Now that we know that you have determined that the Subaru MCs are the same, it makes things more clear.
Brake bleeding is the simplest thing to check / correct, so usually it's one of the first things brought up. Many people screw it up and have issues like you are describing.

Have you contacted Wilwood and asked their opinion on whether or not their MC would be compatible w/the Subaru brakes you have now?

Since you have confirmed the other items, that's what I would do and see what you can find out.

I just don't want to see you spending the time, effort, and money to buy the Wilwood unit only to find that there is little to no improvement.
Yes trying to ask them as well. Agreed I didn't want to bark up the wrong tree and hence trying to see if anyone else had similar experiences when upgrading to significantly larger calipers / number of pistons.
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